The present invention relates to a SCARA robot.
The SCARA robot (Selective Compliance Assembly Robot Arm) is generally known as a robot having multi-joint arms which may be moved in a horizontal plane. More precisely the SCARA robot has a first arm having one end articulated to a mount of the robot and a second arm having one end articulated to the opposite end of the first arm and having an R shaft rotatably mounted on the free end thereof so that the R shaft may be rotationally operated to work. In addition to the three articulation axes, the mount may be moved vertically of the robot body. Thus the robot is generally of three (3) or four (4)-axis type. Conventionally the SCARA robot has been generally operated by the servomotor type of drive sources.
The servomotor is generally big sized and the control device is accordingly required to be big sized. The SCARA robot is, therefore, eventually considerably bulky requiring so much consumption of electric power. Further, the servomotors are normally mounted on the arm side of the robot. The SCARA robot is, therefore, required to be constructed solid and strong enough to support such big and heavy servomotors and the corresponding big sized control device for supplying electric power to the servomotors. This is because the SCARA robot is destined to be bulky.
Instead of the servomotors, stepping motors may be employed to reduce the size of the SCARA robot. However if there is not a position confirmation function provided, it is always required to revert to the initial set at the first step of control routine to control the stepping amount of the stepping motors at each moving step thereof, that is, to control the moving amount of the stepping motors on the basis of a reference position.
Further, the SCARA robot driven by AC servomotors is designed to automatically operate within a predetermined performance area irrespectively of some obstacles or persons that may happen to be within the performance area. This will cause damages to things or hurt the persons. It has been often required to make the indication of "Keep Off".
The invention has been provided to eliminate the defects and disadvantages of the prior art. It is, therefore, a primary object of the invention to provide a SCARA robot which is mechanically compact and small sized.
It is another object of the invention to provide stepping motors for driving the essential elements of the robot.
It is another object of the invention to provide sensors for detecting the moving amount of the steeping motors, thereby to eliminate the necessity of reverting to the initial set at the first step of the control routine of the stepping motors at each moving step thereof, thus to secure the correct movements of the essential elements of the robot.
It is another object of the invention to compare the required moving amount and the actual moving amount of the stepping motors and correct the errors, if any, thereby to secure the correct movements of the essential elements of the robot.
It is another object of the invention to stop the stepping motors if the errors are detected in stepping movement of the stepping motors.
It is another object of the invention to indicate the errors detected in stepping movement of the stepping motors.
It is still another object of the invention to provide a means for driving the stepping motors at a reduced speed to confirm if the essential elements of the robot operates within a predetermined performance area.